The present invention pertains to joining together the leading end of a newly prepared web of material to the trailing end an expiring roll that is being fed to a continuous web processing operation. In particular, the present invention relates to a method and apparatus for evenly splicing a web of layered material, and more specifically a lightweight web material such as an airlaid, nonwoven web, which can be difficult to cut without tearing, so that a web from a new roll of material may be joined via a butt joint to the web of an expiring roll.
Various apparatus and methods for joining or splicing webs used in continuous web processing operations are known in the art. One common method of joining web materials is the lap joint, wherein the leading end of the new web is treated with a suitable adhesive, and at the proper time is manually lapped over the trailing end of the expiring roll. U.S. Pat. No. 4,519,858 describes an apparatus and method for making such lap joints.
A drawback of the lap joint is that it produces an undesirable double thickness of material at the joint. Such double thickness is particularly unsuitable for relatively
A drawback of the lap joint is that it produces an undesirable double thickness of material at the joint. Such double thickness is particularly unsuitable for relatively thick web materials. Furthermore, because of restrictive operations downstream of the joint, certain types of materials, including two-ply pressure sensitive label stock, cannot be spliced in a lap joint
Another common method of joining webs is through the use of a butt joint. With a butt joint, the leading end of the new roll is butted up against, but does not overlap, the trailing end of the expiring roll. An adhesive, such as a relatively thin, single-sided piece of adhesive tape is then used to join the butted ends together.
In the past, hand operations have had to be used to achieve a good-quality butt joint. Typically, a good quality butt joint has less than a one/one thirty-second inch gap between the butted ends of the webs that are being joined. The accuracy required has necessitated the stoppage of the running web from the expiring roll for a sufficient time to make a hand splice. However, as each roll expires, such stoppage results in significant loss of production time.
One apparatus and method for achieving an accurate butt joint is disclosed in U.S. Pat. No. 4,801,342 (“U.S. Pat. No. '342”), which is hereby incorporated by reference in its entirety. U.S. Pat. No. '342 discloses an apparatus wherein a portion of the web from a new roll is held against an anvil, the anvil having a cutting edge disposed at an angle to the path of travel of the expiring web running past the anvil. The invention disclosed in U.S. Pat. No. '342 also includes a knife wheel assembly that is mounted to one side of a splice wheel arm, the other end of the splice wheel arm being pivotably connected to a pneumatic cylinder. The knife wheel assembly includes a roller that has an axis that is perpendicular to the side of the anvil. The upper portion of the roller is a rotary or round knife that is aligned with the cutting edge of the anvil and which is perpendicular to the anvil's sides. As the pneumatic cylinder pivotably moves the splice wheel arm, the roller rotates against the web material that is being held against the adjacent side of the anvil. The rolling motion of the roller rotates the rotary or round knife along the cutting edge of the anvil, thereby trimming or cutting the web material so that the trimmed edge of the trailing or leading end of the web is aligned with and congruent to the cutting edge of the anvil.
The apparatus and method disclosed in U.S. Pat. No. '342 works very well for forming a butt joint for die cut, self-adhesive label stocks and heavier weight web stocks. However, for lighter weight webs, such as tissue or layered webs, including nonwoven airlaid webs, it is sometimes difficult for the device taught in U.S. Pat. No. '342 to evenly cut the web material without tearing. With such lightweight materials, the roller is often pushed, rather then rolled, across the web material that is being held against the adjacent side of the anvil, thereby causing the round or rotary knife to tear, rather than cut, the material. Additionally, in other lightweight web material applications, rather than cutting or trimming the web material, the rotating rotary or round knife merely pushes the material over the side the of the cutting edge of the anvil.
One alternative approach has been to utilize a hot wire to evenly cut or trim the web material. The use of a hot wire, however, can ignite materials that have some cellulose content, such as airlaid webs.
There is, therefore, a need for an improved apparatus that will evenly cut lighter-weight webs and permit such webs to be joined with a high-quality butt joint, while at the same time retaining all the commercial advantages achieved by the apparatus and method disclosed in U.S. Pat. No. '342.
Accordingly, it is an object of the present invention to provide an improved apparatus for forming a good-quality butt joint to join lightweight or layered webs, such as tissue or airlaid webs.
It is another object of the present invention to provide an improved apparatus for forming a butt joint that can cut lightweight or layered webs without tearing so that the web is evenly cut and can be joined to another web via a butt joint.
It is another object of the present invention to provide a method for accurately trimming or cutting lightweight or layered web materials without tearing so that a web material can be joined together via a butt joint.
These and other objects and advantages are provided by an improved apparatus and method for forming a butt joint that employs an anvil having a cutting edge and a shear wheel having a rotary cutting edge, and in which the rotary cutting edge rotates with the shear wheel and cuts a web along the anvil cutting edge when the web is secured against the anvil. The improvement comprises driving the shear wheel to ensure that the shear wheel is rotating as it moves across web material that is being held against the side of the anvil. In one embodiment, the improvement comprises wrapping a spring loaded shear wheel with a drive cable that is under tension to cause the shear wheel to positively rotate. In such an embodiment, the shear wheel may be provided with a circumferential groove that is configured to receive at least a portion of the drive cable and to prevent the drive cable from slipping off the shear wheel. Alternatively, the shear wheel may be operably driven via a gear drive, belt drive, or direct drive, such as a motor, configuration that ensures that the shear wheel positively rotates. The forced rotational speed of the shear wheel permits the rotary cutting edge to evenly cut or trim lightweight or layered webs without tearing.